Efforts to use renewable energy are gaining momentum, year by year, toward reducing emissions of CO2 being one of main substances for global warming, and supplying energy stably. Especially, wind power generation is focused on from the viewpoints of stability and profitability, and most of all, the amount of introduction of offshore wind turbines is expected to increase in the future for an increase in scale and the stabilization of the volume of air.
However, the offshore wind turbines have an issue that the maintenance cost increases compared to land wind turbines. Especially, in an AC excited generator used in many cases as a generator for wind power, electric power is supplied to a rotor through a brush. Accordingly, the wear of the brush and electrolytic corrosion occur, and the frequency of maintenance increases, which spurs the increase of costs.
For example, in PTL 1, a brushless AC excited generator is described with the object of providing a rotating electrical machine and the like that can improve power generation efficiency while facilitating maintenance.
The publication discloses a configuration in which a rotating exciter and an electric power converter are provided coaxially with the AC excited generator, the power of an electric power system is rectified to direct current, a stator of the rotating exciter is brought into conduction, the power is supplied to a rotor by the principle of the synchronous generator, and then the electric power converter supplies the power the power whose voltage and frequency have been converted to a rotor of the doubly fed synchronous generator to perform a power generation operation. According to the configuration, the electric power converter is attached to the rotor. Accordingly, the electric power converter rotates with the rotation of the rotor. It is described that the electric power converter requires control in accordance with the rotation of the wind turbine, and control signal transmission by optical communication is used to receive a control signal brushlessly.
Moreover, PTL 2 discloses a wireless communication technology of a rotator. A plurality of antennas is arranged at at least one of a rotator and a stator in at least a substantially regular distribution in a direction along the periphery of rotation. The plurality of antennas is connected in parallel to a transmission apparatus or receiving apparatus.
The lengths of the antennas overlap in the direction along the periphery of rotation. These antennas are offset at least partially in the direction of the radius or length of a rotation shaft, and arranged. The transmission apparatus supplies a signal phase-shifted by a delay element to each antenna. The receiving apparatus causes a delay element to phase shift and superimpose the signals received at the antennas. In other words, it is described that even if there is a null point in the directivity of one antenna on the rotator side or stator side, the signal strength can be increased by combining the received signals of the plurality of antennas arranged regularly on the other side.